1. Field of the Invention
This invention relates to devices for ascending stairwells that employ a “cluster,” “X,” “Y,” “spider,” or “wheel-over-wheel” assembly.
2. Description of the Related Art
Towing items such as suitcases and luggage have limited facilities when traversing stairwells. While ascending/descending stairwells, the owner of the towing device has to lift it up and over the corner of each step rendering the wheels useless in this situation. This also leads to a jerking motion as the towing device hops from stair to stair.
Conventional luggage has shown the inclusion of skids on the back of the suitcase panel to ease the suitcase sliding up the stairs. However, these skids typically wear down with use, and not as frictionless as they need to be. Conveyor belts have been proposed: U.S Published Application No. 20040094378 describes a motorized suitcase with brake that utilizes tank treads and rollers. Conveyor belts generally lack adequate grip on stairwells for personal suitcases since the unit may only be in contact with the leading edges of 2-3 stairs at most. Such units must lay flat along the stairs and be heavy enough to create a downward force for the tank treads to effectively grip the stairs and require an overly-lengthy handle for proper use.
Other devices that employ “spider wheels,” “cluster wheels,” or “wheel over wheel,” mechanisms for stair climbing are known. Such devices utilize small, freely-rotating wheels fastened at the ends of spokes that rotate all together as a rigid assembly. PCT Patent Publication No. WO8600587A1 describes a stair-climbing hand truck utilizing rotating spider wheels. Spider wheel assemblies, however, protrude from the main body of a towing device, reducing overall portability.
U.S. Pat. No. 6,484,829, a battery powered stair-climbing wheelchair utilizing two sets of wheel-over-wheel assemblies is described. In that particular vehicle, however, the design addresses mechanisms that controls pitch and attitude adjustment for complete support, orientation, and self-propulsion of human beings up and down stairwells. The preferred embodiment of that vehicle does not include any means of rendering the cluster wheel foldable or collapsible for portability.
This invention introduces a collapsible spider wheel assembly, rendering the towing device to which it is attached, portable for transport. Such towing devices may include but is not limited to: suitcases, hand trucks, and baby strollers.